1. Field
This disclosure relates to a load bearing compressed gas tank mounting structure for motor vehicles.
2. General Background
Pressurized cylinder failure is measured in terms of burst pressure. If a cylinder has a 3000 psi rating it will have a burst strength (or failure rating) of 2-3 times that normal 3000 psi rating.
Pressurized cylinders are useful; for storing and transporting fuels such as hydrogen, natural gas (CNG) and propane.
Storage of gaseous fuel cylinders/tanks in a tractor or trailer must meet crash safety requirements.
Tractor Trailers have many different weight ratings which may affect their usage and the cost of usage.
Gross Vehicle Weight (GVW). This is the total weight of the loaded vehicle. This includes the vehicle itself and the cargo that is loaded on the vehicle.
Gross Combination Weight (GCW). This is specified by the manufacturer as the maximum loaded weight of a truck/tractor plus the trailer or semi-trailer designed for use with the truck/tractor.
Gross Vehicle Weight Rating (GVWR). This is the rating that is calculated by the manufacturer as the amount of weight that the vehicle will be when the vehicle itself is weighed, filled with fuel, and loaded according to the manufacturer's specification.
Gross Combination Weight Rating (GCWR). This is the maximum allowable combined mass of a towing road vehicle, passengers and cargo in the tow vehicle, plus the mass of the trailer and cargo in the trailer. This rating is set by the manufacturer.
Safety Compliance Weight. The Federal Motor Carrier Safety Regulations (FMCSRs) have two definitions of a Commercial Motor Vehicle (CMV) for interstate carriers; each definition applies to specific safety regulations. Sec. 390.5 defines the weight of a CMV as 10,001 lbs. or more GVW/GCW or GVWR/GCWR. In this situation, the FMCSA may use either the GVW or the GVWR (whichever is highest). If the actual GVW of the vehicle is 9,150 lbs. but it has a manufacturers' GVWR of 10,500 lbs., it is a CMV subject to the rules. The definition in Parts 382 and 383 says a CMV is 26,001 or more lbs. GCWR or GVWR. In this case, only the manufacturers' weight rating matters. The actual gross vehicle weight is not a factor in determining compliance. When a state adopts the FMCSRs for their intrastate carriers, a different weight threshold may be adopted for intrastate compliance.
Registration Weight. The registered weight of a vehicle is not related to any compliance with the FMCSRs. A vehicle must be registered for the actual gross weight or combined gross weight. This means the empty weight of the vehicle plus the empty weight of any towed vehicle, plus the weight of the heaviest load to be carried. Generally, vehicles should not be registered for a weight higher than the weight rating; most states will not allow registration exceeding the weight rating. If the vehicle travels on the highways at a weight higher than the registered weight shown on the registration, a citation may be issued for overweight on vehicle registration.
Any vehicle operating interstate with a GVW or GCW or registered weight of 26,000 lbs. or more, or having three axles at any weight, is subject to the International Registration Plan (IRP) for apportioned registration and the International Fuel Tax Agreement (IFTA) for payment of fuel use taxes. These base state agreements do not use the vehicle weight rating when determining compliance.
Highway Weight. This is the legal weight related to highway size and weight limits. When operating on the interstate system, the maximum permissible weight is 20,000 lbs. on a single axle, 34,000 lbs. on a tandem axle, and 80,000 lbs. max gross weight. The “Bridge Formula” allows motor vehicles to be loaded to the maximum weight only if each group of axles on the vehicle and their spacing also satisfy the requirements of the formula. States must use these limits for their designated or national network highways. While the majority of the states use the federal bridge formula for all roads in their state, some do have a separate state formula for other state or county roads. Tare weight is measured and a truck can be penalized for higher Tare weights.
National Fire Protection Agency “NFPA” 52: VEHICULAR GASEOUS FUEL SYSTEMS CODE “safeguards people and installations with requirements that mitigate the fire and explosion hazards associated with compressed natural gas (CNG) and liquefied natural gas (LNG) engine fuel systems and fueling facilities.”
Section 6.3.4 of the code specifies that each fuel supply container rack shall be secured to the vehicle body, bed, or frame to prevent damage from road hazards, slippage, loosening, or rotation using a method capable of withstanding a static force in the six principal of eight times the weight of a fully pressurized container(s).
Moreover section 6.3.5 specifies that each fuel supply container in the rack shall be secured to its cradle in a manner that it is capable of withstanding a static force, applied in the six principal directions of eight times the weight of the fully pressurized container with a maximum displacement of 0.50 in. (13 mm).
A traditional rack and tank support system provides a steel rack/cage with compartments to hold tanks to meet such safety standards and bear loads.